Why? Able to read only 1 bytes on GPIB at query.

Hi.

I able to read Only 1 bytes on GPIB at query to keithley2182(NanoVoltMeter) and keithley6221(AC/DC SourceMeter).

For example, Reading buffer after has written "*IDN?", could reading "K". And then read "E", "I"... every time when I push only "Read".

Actually I should get whole of instruments identification;"KEITHLEY INSTRUMENTS..." when I push "Write"and"Read" once.
But It had been useless chaging GPIB cable, rebooting my PC and instruments.

On the other hand I could get whole of identification on other instruments (example:keithley7001,6510 and Lakeshore340) when I pushed once.

Why I connot get whole id?
Please help me.

(Postscript. It are so terrible that my English, but your consideration make me happy. Thank you for reading.)